astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.
black hole: A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.
celestial: (in astronomy) Of or relating to the sky, or outer space.
celestial object: Any naturally formed objects of substantial size in space. Examples include comets, asteroids, planets, moons, stars and galaxies.
constellation: Patterns formed by prominent stars that appear to lie close to each other in the night sky. Modern astronomers divide the sky into 88 constellations, 12 of which (known as the zodiac) lie along the sun’s path through the sky over the course of a year. Cancri, the original Greek name for the constellation Cancer, is one of those 12 zodiac constellations.
galaxy: A group of stars — and usually invisible, mysterious dark matter — all held together by gravity. Giant galaxies, such as the Milky Way, often have more than 100 billion stars. The dimmest galaxies may have just a few thousand. Some galaxies also have gas and dust from which they make new stars.
gravitational lens: The distortion of light by an intense gravitational force, such as what can be exerted by a supercluster of galaxies — the most massive things in the universe. The gravity can bend or focus light, making it appear brighter and in one or more different places in the sky.
gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
journal: (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. Peer-reviewed journals are the gold standard: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or work that is not novel or convincingly demonstrated.
light-year: The distance light travels in one year, about 9.46 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.
mass: A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
Milky Way: The galaxy in which Earth’s solar system resides.
neutron star: The very dense corpse of what had once been a massive star. As the star died in a supernova explosion, its outer layers shot out into space. Its core then collapsed under its intense gravity, causing protons and electrons in its atoms to fuse into neutrons (hence the star’s name). A single teaspoonful of a neutron star, on Earth, would weigh more than a billion tons.
orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.
rogue: An animal that wanders alone, outside its herd or the community into which it was born. Or anything, even a planet or galaxy, that unexpectedly travels alone and far from where it would be expected.
solar: Having to do with the sun or the radiation it emits. It comes from sol, Latin for sun.
star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun: The star at the center of Earth’s solar system. It is about 27,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
uncertainty: (in statistics) A range of how much measurements of something will vary around an already-measured value.